Supersonic apparatus



April 24, 1945. v||. c. HAYES SUPERSONIC APPARATUS 2 Sheets-Sheet 1 Filed Sept. l0, 1931 INVENTOR S 6 WM a W V W Hw Vl B ATTORNEY April 24, 1945. Q HAYES 2,374,637

SUPERSONIC APPARATUS Filed sept. 1o, 1951 "2 sheets-sheet 2 v51/LA 750 powa INVENTOR Harveyf C'. Hayes ATTORN EY Patented Apr. 24, 1945 UNIT@ STATES @ATNT FMC@ SUPERSGNIC APPARATUS Harvey C. Hayes, Washington, D. C.

Application September l0, 1931, Serial No. 562,183

(Granted under the act o March 3, 1883, as amended April 30, i928; 374i 0. G. 75?) l l Claims.

rI'his invention relates to improvements in supersonic apparatus and particularly to a construction of sound transmitters and receivers which results in greater eciency and reliability than has been had in apparatus heretofore available.

The objects of my invention are, rst, to reduce internal losses resulting from the tangential or shearing forces along the surface of the plates, which forces are set up by the change in dimension of the crystals along the y-axis, caused by the change in field along the iz-axis;

Second, to eliminate the loss due to friction between the inner plate and the insulating wedges;

Third, to eliminate the spun metal cap and to provide a steady pressure against the back of the plate to assure its positioning against the crystals;

Fourth, to provide a'molecular contact between the crystals and `the plates that is not destroyed by the jars incident to service or an arcing between the plates.

With the above and other objects in view, the invention consists in the construction, combination and arrangement of parts as will be hereinafter more fully described.

Reference is to be had to the accompanying drawings forming a part of this specification in which like reference characters indicate correspending parts throughout the several views and in which: n

Figure l is a section of a sound transmitter and receiver;

Figure 2 is a section through Figure l;

Figure 3 is a side elevation of Figure 4 with the top plate removed;

Figure 4 is a section of my improved sound transmitter and receiver;

Figure 4A is a sectional view through the modification of the improved sound transmitter and receiver illustrated in Figure 4.

In Figure 1, reference number II) `is a cupshaped casting provided with an outlet neck Il through which an insulated lead I2 may enter through a water-tight stuffing-box and which carries a ange I3 by which the casing canbe secured to any similar member, for instance, a periscope tube carrying at its end a similar flange. The rim of the cup is threaded to carry a threaded iiange I4 designed to compress the disk-shaped member I5 between gaskets I6 and l'i to maintain water-tight integrity within the cup. Members I5 and I8, except for the ange on I5,`are preferably identical as to thickness and material. They are metal disks with planes parallel and with circular faces. These plates are separated by a mosaic of pieno-electric crystals 23 ground to uniform thickness and the Whole combination, plates with intervening crystal mosaic, is solidly stuck together by means of a, suitable cement or wax. The inner plate i8 carries a spun or pressed thin metal cap I9 which assures that the plate shall be backed by a layer of air 2li when the space 2l is filled with grease or a low-melting wax. Three or more insulating wedges 22, placed between plate i8 and case il) help to support plate i8 so that the wax or cement which holds the combination i5, i8, 23 together need not bear the entire weight of plate i8. The electrical lead I2 connects with plate i3 which is insulated from all its surroundings. Plate i5 either directly or through water is `grounded to case il).

plate I3 and in Athe central portion shows the nature of the quartz mosaic with plate i5 removed. Also, the circumferential location of the insulating wedges 22 is shown.

The principle of operation of asubmarine sound transmitter and receiver, such as shown in Figures l and 2, iswell known in the art and brieiiy is as follows: If the quartz crystals are cut so that the direction through them and perpendicular to the faces of the plates I5 and I8 is alike for each and along the z-axis of the crystal, then an alternating or fluctuating electric potential connected across the two plates I5 and I8 will expose the crystals to a varying electric ileld directed along their :lz-axis, and they will suffer changes in thickness in conformity with and in proportion to the variations of the electric field across them, or in other words, to the voltage variations across the two plates. If the voltage variations are made periodic and of the proper frequency the two plates with the intervening crystals will be thrown into oscillation as shown schematically by curves 24' and 25 of Figure 1. This is the natural or fundamental frequency of the plate-crystal combination and it is obvious that it could be oscillated at the odd harmonics of this frequency. The outside surface of plate I5, which is in contact with the water, generates the submarine sound.

Both laboratory and eld tests have shown that the internal losses can be materially decreased and the generated sound energy correspondingly increased by a proper design and arrangement of the crystal mosaic, 'Ihe explanation of this is as follows: The crystals must be out as described, so that the electric axis is parallel with the electric field between the plates, and this leaves the pressure or y-axis and the optical or z-axis parallel with the surfaces of the plates. It is well known that a change in eld strength along the :c-axis causes a change in length along both the :zz-axis and the y-axis, the change per unit length along both axes being practically the same. This results in a y-movement along the surface of the plates which is normally great compared with the :r-movement because the :li-dimension is much greater than the thin :c-direction. Such motion creates tangential or shearing forces along the plate surfaces which tend to tear the quartz loose from the plates or at best to generate considerable heat along the surface planes which softens the wax to the point where it allows the plates to separate. It is obvious that the magnitude of such losses will increase with the dimensions of the crystals with respect to the y-axis and would become a maximum if the whole plate surface were covered by a singie-crystal. It follows that the magnitude of such internal losses will not be the same for two transmitters having plates of the same area, but provided with mosaics of different shaped and diierent sized crystals. The improvement which overcomes this difllculty is explained in connection with Figure 3 which shows a. transmitter similar to Figure 2 with the exception that the mosaic is made of crystals cut to equal size and shape and having the angular relation between faces, edges and crystallographic axes in all crystals the same. In the construction shown the crystals are cut to square form with Vthe y-direction corresponding to two opposite sides ofthe square and the z-direction to the other two sides. The .1c-direction is perpendicular to the plane of the paper. The best arrangement is had by placing the crystals so that the y-axes of any'two ,adjacent crystals make an angle of ninety degrees with one another. Sincevthe expansion along the z-axis is practically zero under the action of an electric that in this way the, retaining point or points which hold the oscillating system centered are located very near the nodal plane. It is obvious that the scheme of holding the plates centered axially by retaining them `against each other rather than by anchoring each against'the case, can be carried out in other ways, as illustrated in Figure 4A for instance, wherein an insulated dowel or dowels 2l pass from the plate I 5 through the crystals 23 into the other plate I8. A neatly tting band 26, made of insulating material, which will slide over the inner rim of both plates I5 and I 8 with the crystal mosaic 23 intervening is also provided. While both the dowel and ring means have been shown in the single modiiication illustrated in Figure 4A, it is obvious that either one would be suilcient. The construction shown n Figure 4 and Figure 4A permits of accurate lining up of the oscillating system upon assembling and serves to keep them in alignment against jars and yielding of the wax or cement with time.

The construction shown in Figure 4 and Figure 4A has another improvement in that it eliminates the spun metal cap I9 and provides a steady pressure on the back of plate I 8 so as to assure the positioning of this plate against the crystals by overcoming the separating action of its own weight and such jars and jolts as may be met in practice. This is accomplished by placingva rubber ring 25 between plate I8 and the back of case I0, the ring having dimensions such that it ts about the circumference of the plate and is compressed between the plate and case as shown. This construction reduces the cost oi production and makes operation more sure by holding the inner parts rigidly in position. The space 2l can be iilled with wax or grease as used in the construction of Figure 1.

Still another improvement has to do with the field as compared with that along the y-axis, this arrangement gives the minimum shearing motion along the surface of the transmitter when vconsidered for all directions along the surface.

In fact, it gives a uniform shear in all directions along the surface. In Figure 3 the arrows repy resent the directions of the y-axes for the several crystals of the mosaic. Other forms than a square. might be employed and would serve as well, but the cost of cutting crystals having the shape of a hexagon or the like would be more expensive.

The second improvement has to do with the elimination of the retaining wedges 22 which prove difdcult to locate properly when assembling the apparatus and which at best fail to keep plate I8 pressed against. the crystals. Since the combination I5, 23.18 oscillates as a solid mass with a node in the midplane of the crystals, it is obvious that any supporting flanges or centering members should be placed as n ear as possible to this nodal plane to prevent damping losses, 'Ihe wedges 22 introduce such losses because the cylindrical surface of the plate I8 has to rub back and forth along the surface of contact. Figure 4 shows an improvement on this construction. The plates I5 and I8 are machined and ground so that the faceeXpOsed to the quartz crystals carries anarrow edge 24 that projects about a millimeter out from the surface against which the crystals are mounted. As a result the plate I8 cannot shear across plate I5 because of the insetting oi' the crystal mosaic, and it is to be noted binding together of the two plates and the crystal mosaic. The wax or cement assembly described in connection with Figure l proves in practice to have three weaknesses.v First, the plate and crystal combination separates-under the action of slight sharp jars or of the heat generated when the device is driven under high electrical potentials so as to give intense sound signals. The amplitude of motion of the quartz crystals is so small that no sound energy is generated unless the whole combination is held in strict molecular contact and as a result the mere pressing together of the combination'is not suflicient to make it function if the adhesive contact between wax and quartz or steel is broken; the wax must be remelted and allowed to harden before it will function. No wax or cement has been found that will not break at the surfaces of contact under the action of a short sharp blow and as a result the transmitters have not been considered thoroughly reliable for use on ship board. The second weakness lies in the fact that if the voltage across the plates happens to become suiliciently high to spark or arc across, the plates remain short circuited and useless because of the carbonization of the wax along the spark path. Such accidents often happen due to voltage surges when the circuit is broken and require that the whole combination be cleaned and reassembled. The third weakness lies in the fact that the natural frequency of the transmitter varies considerably with change in temperature, tending to become lower as the temperature is raised and vice versa.

The first two Weaknesses have been entirely overcome and the third one greatly improved by replacing the cement or wax used to bind the plates and quartz together with an oil oi high insulating qualities and proper viscosity and capillary activity. Since the liquid wets the plate and quartz surfaces the condition of true molecular contact is always met and if the surfaces are ground and polished to an optical plane the thin oil nlm between metal and quartz is as rigid as regards the transmission of high frequency sound waves as is a wax or cement. Moreover, if a spark passes between plates and through the oil nlm it immediately heals over without leaving the plates short circulted. Thus, the first two weaknesses which have tended to make transmitters unreliable have been completely overcome. The change in frequency of the transmitter with varying temperature has been practically eliminated by a proper choice of oil. The thickness of the oil iilm separating the quartz and the metal is dependent upon the capillary force tending to pull the oil between the surfaces and also upon the pressure exerted by the rubber ring 25 which forces the surfaces together. The latter force is sensibly constant. The capillary force decreases as the temperature increases and as a result the thickness of the oil nlm varies somewhat inversely with the temperature, becoming thinner as the mperature rises and thicker as it falls. It is obvious that the natural frequency or the transmitter increases as the perpendicular distance between the outer face oi l and the inner face oi l decreases. It will thus be seen that the change in thickness ci the oil iilms brought about by change in temperature is in the proper direction to comnsate for the change in equency incident to the change in temperature. This compensation can be practically effected by choosing an oil having the proper capillary activ ity and a rubber ring which-furnishes a proper amount oi pressure between plates. A mixture of one-fourth linseed oil and three-fourths castor oil works well.

It will be understood that the above description and accompanying drawings comprehend only the general and preferred embodiment of my invention, and that various changes in construction, proportion and arrangement of parts may be made within the scope of the appended claims, and without sacriiicing any of the advantages of my invention l The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

I am aware that prior to my invention supersonic transmitters and receivers have been constructed o metal plates with quartz crystals intervening. I therefore do not claim such a combination broadly; but I claim:

1. In a supersonic signaling device comprising an inner and an outer metallic plate with a mosaic of intervening quartz crystals, a method of reducing internal losses consisting of cutting the crystals to the same size and 'shape and so that in all crystals the angular relation between faces, edges and crystallographic axes is the same, and molmting said crystals between metallic plates so that the y-am's of each crystal is at right angles to the y-axis of any adjacent crystal.

2. In a supersonic signaling device comprising an inner and an outer metallic plate with a mosaic of intervening quartz crystals, a method of reducing internal losses consisting of cutting the crystals to the same size and shape and s0 that in all crystals the angular relation between faces, edges and crystallographic axes is the same, and

mounting said crystals between metallic plates so that the y-axis of a part of the crystals are in one direction and the y-axes of the remainder of the crystals are in a direction making an angle of substantially ninety degrees with the rst direction, the crystals associated with each direction being intermixed.

3. In a supersonic signaling device comprising an inner and an Vouter metallic plate with a mosaic of intervening quartz crystals, aV method of reducing internal losses consisting of cutting the crystals to square form with the L1-direction corresponding to two opposite sides of the square and the z-direction to the other two sides, the :fc-direction being perpendicular to the plane of the square and mounting the crystals between the metallic plates so that the y-axes of any two adjacent crystals make an angle of ninety degrees with one another.

e. In a supersonic signaling device comprising an inner and an outer metallic plate with a mosaic of intervening piezo-electric crystals, a method of reducing the loss due to the shearing forces along the surfaces of the plates caused by the motion oi the crystals, consisting of making the crystals as small as practicable, cutting the crystals to the same size and shape and so that in all crystals the angular relation between faces, edges and crystallographic axes is the same, and mounting the crystals between metallic plates so as to obtain a uniform shear in all directions along the surfaces of the plates.

5. In a supersonic signaling device comprising an inner and an outer metallic plate with amosaic of intervening quartz crystals Whose :r-aXes are perpendicular to and y-axes parallel with the surfaces of said plates, a method of reducing the loss due to the shearing Yforces along the surfaces of the plates caused by the motion of the crystals, consisting of making the crystals as small as practicable, cutting the crystals to the same size and shape and so that in all crystals the angular relation between faces, edges and crystallographic axes is the same, and mounting the crystals between the metallic plates so that the y-axes of any two adjacent crystals are at an angle to each other, whereby a uniform minimum shear in all directions along the surfaces of the plates is obtained.

6. In an ultra-audible sound signaling device comprising a containing case, an inner and an outer metallic plate with a mosaic of intervening piezo-electric crystals positioned within said case and secured thereto so that thel back surface and peripheral sides of said inner plate form a void with said case, means for maintaining an air layer at the back of the inner plate when said void contains an insulating medium consisting of a rubber ring whose thickness is such that it is compressed between the back of the inner plate and case and wh'ose diameter is such that it ts about the circumference of the inner plate.

7. In an ultra-audible sound signaling device the combination of an inner and outer plate with a. mosaic of intervening piezo-electric crystals, an edge on each plate extending around the circumference and projecting out from the surface against which the crystals are mounted so as to embrace the crystals, a containing case for said plates and crystals so constructed as to leave a small space between the back of the inner plate and the back of the case, and a rubber ring whose outer diameter is substantially the same as the diameter of the inner plate and which is concentrically placed on and compressed between the back of said inner plate and the case.

8. A supersonic signaling device comprising an outer and an inner metallic plate, a mosaic of piezo-electric crystals interposed between the plates, an oil for assuring adhesion between the contact surfaces of the plates and crystals, said oil being of proper viscosity and capillary activity whereby with change in temperature the thickness of the oil lm between the plate and crystal surfaces compensates for the change in thickness of the plates and crystals maintaining a. constant natural frequency in the plate-crystal combination.

9. In a supersonic signaling device comprising an'outer and an inner metallic plate with a mosaic of intervening piezo-electric crystals, an oil for assuring adhesion between the contact surfaces of the plates and crystals, said oil having high insulating qualities and proper viscosity and capillary activity, and means for applying through an elastic substance a pressure to the back of the inner plate, whereby a break in said contact surfaces created by shock is automatically renewed, a rupture in the oil film caused by high potential across the plates is self healed and change in thickness of the plates and crystals due to change in temperature is compensated for.

10. A supersonic signaling device comprising an inner and an outer metallic plate, a mosaic of piezo-electric crystals interposed Lbetween the plates and liquid means for assuring adhesion between the contact surfaces of the plates and crystals, said liquid means containing substantially one-fourth linseed oil and three-fourths castor oil.

11. In a supersnic signaling device, a cupped 4shaped containing and supporting member, an

inner metallic plate, an outer metallic plate, a mosaic of piezo-electric crystals interposed between said plates, means securing and hermetically sealing said outer plate to said cup member to maintain a water-tight integrity within said cup, means supporting said inner plate at substantially the nodal plane of the plate crystal combination so that said plate will be spaced from said cupped member and its vibrations undamped by surface contact therewith, anoil hn of high insulating qualities between said plates and crystals for maintaining molecular contact between the surface of the said plates and the crystals,

means comprising an insulating medium having a low coefficient of friction positioned within the space between said plate and crystal combination and the walls of said cupped member for maintaining said oil fllm between said plates and crystals, and means providing an air layer back of said inner plate when the space contains said medium and producing a pressure against the back oi the inner plate.

12. The combination as deilned in claim 11 wherein said second named means comprises a narrow edge extending around the periphery of each plate which edges project out from the surfaces against which the crystals are mounted so as to embrace the crystals to prevent the inner plate from shearing across the outer plate and to maintain the plate-crystal combination in alignment.

13. The combination as defined in claim' 11 wherein said last named means comprises a resilient gasket conforming substantially to the shape of the inner plate compressed .between the back of the inner plate and the cupped member.

14. In a supersonic signaling device a'cupped shaped containing and supporting member, an inner metallic plate, an outer metallic plate, a mosaic of piezo-electric crystals interposed between said plates with their :r-axes perpendicular thereto, means comprising an oil illm positioned between said plates having a viscosity and capillary activity which produces a change in the thickness of the oil film substantially equal and opposite to the change in thickness of the crystal-plate combination with equal changes in temperature, whereby the overall thickness will remain substantially constant irrespective of operating temperature.

15. In a supersonic signaling device a cupped shaped containing and supporting member, an'

inner metallic plate, an outer metallic plate, means securing said outer plate to said cupped member, and a mosaic of piezo-electric crystals interposed between said plates, said mosaic comprising a plurality of equal sized similarly shaped crystals having the same angular relation between faces, edges and crystallographic axes, each crystal being arranged with its :r-axis perpendicular to the vsurface of said inner and outer plate and with its y-axis positioned at an angle of ninety degrees relative to the yfaxis of an adjacent crystal.

' HARVEY C. HAYES. 

